This application claims the priority of German Application No. 101 60 266.9, filed Dec. 7, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and an arrangement for supplying quiescent current to a vehicle having a multi-voltage on-board electrical system with at least two on-board electrical subsystems.
A conventional multi-voltage on-board electrical system is known, for example, from German Patent DE 199 21 451 A1. The multi-voltage on-board electrical system of this reference includes a plurality of on-board electrical system circuits or on-board electrical subsystems having power supply sources which have different voltages intended for respective different loads. Decentralized electronic controllers for controlling and regulating associated loads are supplied with power by means of the on-board electrical subsystems. Depending on the type and design of the multi-voltage on-board electrical system, the on-board electrical subsystems are supplied with power by a common generator which supplies power directly to one of the on-board electrical subsystems, in particular the on-board electrical subsystem for high-consumption loads and for the starter region. This on-board electrical subsystem is assigned its own battery, for example, a 36 V battery in the case of a 42 V on-board electrical subsystem. The 14 V loads which are associated with a further on-board electrical subsystem are connected to the generator via a DC voltage transformer, referred to as a DC/DC transformer. This on-board electrical subsystem has its own associated battery, in particular a 12 V battery. In vehicles with a high level of equipment, such interconnection and decentralization of electronic controllers leads to problems with a long-term energy supply from the battery, in particular to problems with what is referred to as the wake-up capability of the controllers when the vehicle is inactive for a relatively long time, for example at airports.
In order to maintain the wake-up capability of the controllers, they are usually supplied with a low current when the vehicle is stationary. If a controller is then woken up, whether as a result of an external process, for example, a closing process, or as a result of an internal fault, the controllers are automatically woken up and activated by means of a bus system, for example, a CAN bus. This leads to increased power drain and to a significant reduction of the energy reserves. In order to stabilize the on-board electrical system voltage during peak current demand, in a two-voltage on-board electrical system, a battery, which has a high voltage level and is not used for supplying quiescent current, is generally employed. In order to supply quiescent current, in particular a further battery with a lower voltage is used. In order to supply quiescent current in such a way, the controllers with the relatively high voltage are additionally connected by cables to the energy storage means of the on-board electrical subsystem with the low voltage. This leads to a particularly complicated cabling arrangement. Furthermore, this does not eliminate the problem of faulty controllers leading to the waking-up of the bus system and thus to the activation of all the controllers.
It is therefore an object of the present invention to specify a method for supplying quiescent current to a vehicle having a multi-voltage on-board electrical system having at least two on-board electrical subsystems which have different voltage levels during normal operation, and which permits the entire multi-voltage on-board electrical system to be provided with the lowest possible quiescent current in the simplest possible way and with the smallest possible degree of expenditure on cables. Furthermore, it is an object to provide an arrangement for supplying quiescent current which is particularly simple in design.
According to the invention the quiescent current is supplied in such a way that, when the engine is stationary, the voltage levels of the on-board electrical subsystems are reduced to a uniform value. By uniformly reducing the voltage level in such a way in all the on-board electrical subsystems, there is no requirement for separate cabling of loads with a battery to ensure the supply of quiescent current. Furthermore, the direct connection of one of the on-board electrical subsystems to the other on-board electrical subsystem or subsystems permits all the loads, and thus also their controllers, of all the on-board electrical subsystems to be supplied. The uniform value expediently corresponds approximately to the value of the lowest voltage level of all the on-board electrical subsystems. As a result, on the one hand, the lowest possible quiescent current drain is ensured and, on the other hand, it ensures that the battery which covers the peak current demand is not required for supplying quiescent current. The voltage levels are preferably reduced to a uniform value of approximately 6 V to 14 V. It is thus also possible to supply loads with a relatively high voltage. In the case of a quiescent current supply, a resultant relatively slow response, possibly also with reduced effect, is sufficient.
The on-board electrical subsystems are preferably isolated from the respectively associated energy storage device and are connected to one another by connection element in such a way that the charge is drawn from the energy storage device which ensures the quiescent-current operating mode. This is a particularly simple embodiment which avoids complex cabling.
Also provided according to the present invention is an arrangement for supplying quiescent current in a multi-voltage on-board electrical system having at least two on-board electrical subsystems which have different voltage levels during normal operation, in which case, when the engine is stationary, an isolator element isolates the on-board electrical subsystems from the respectively associated energy storage devices, and a connection element connects the on-board electrical subsystems to one of the energy storage devices. This ensures that only one of the energy storage devices is used to supply all the loads in the quiescent-current operating mode. Furthermore, the existing cabling can be used. Additional cabling connecting all the loads to the battery ensures that the quiescent-current operating mode is reliably avoided because the on-board electrical subsystems are connected to one another by a simple connection element in such a way that charge is drawn only from the battery which ensures the quiescent-current operating mode.
The connection element is expediently designed in such a way that the on-board electrical subsystems are disconnected during normal operation. The connection element is preferably designed as a semiconductor element having an optimum conductivity property in the quiescent-current operating mode and a very good blocking property during normal operation. The connection element expediently includes at least one diode or at least one transistor element. Depending on the type and design of the multi-voltage on-board electrical system, the on-board electrical subsystems are connected to one another by a diode or by a plurality of diodes connected in series.
During normal operation, the on-board electrical subsystems are preferably connected to one another by a DC/DC transformer. As a result, during normal operation on-board electrical subsystems having different voltage levels are reliably disconnected. In order to connect the on-board electrical subsystems in the quiescent-current operating mode, the connection element is preferably arranged in parallel with the DC/DC transformer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.